title: Activation of a K+ conductance by bradykinin and by inositol-1,4,5-trisphosphate in rat glioma cells: involvement of intracellular and extracellular Ca2+.
abstract: Extracellular application of bradykinin and injection of inositol-1,4,5-trisphosphate (Ins-P3) induced a hyperpolarization in polyploid rat glioma cells. Ins-1,4,5-P3 and Ins-2,4,5-P3 were effective but not Ins-4,5-P2, Ins-1,3,4,5-P4 and Ins-1,3,4,5,6-P5. The reversal potential of the hyperpolarizing response induced by bradykinin or by Ins-P3 increased to a comparable degree with increasing the extracellular K+ concentration. Certain blockers of K+ channels, for example charybdotoxin (5-50 nM), Ba2+ (5-20 mM), 4-aminopyridine (5-10 mM) and quinidine (0.1-0.5 mM) reversibly suppressed the membrane potential response to bradykinin or to Ins-P3; however, apamin (1 microM) and D-tubocurarine (0.5 mM) had no effect. Intracellular injection of EGTA made the glioma cells unresponsive to bradykinin. Superfusion of the cells with Ca2(+)-free medium gradually and reversibly abolished the response to bradykinin, but only slightly reduced the effect of Ins-P3. The Ca2+ channel blockers Co2+ (1-5 mM), Mn2+ (2-6 mM) and nifedipine (1-20 microM), but not desmethoxyverapamil (100 microM) inhibited the hyperpolarizing effect of bradykinin. The hyperpolarization induced by Ins-P3, however, was not influenced by Mn2+ (1-5 mM) or by Co2+ (7 mM). Injection of Ca2+ into the glioma cells induced a hyperpolarization susceptible to Ba2+ and quinidine. Treatment of glioma cells with an activator or with inhibitors of protein kinase C or with pertussis toxin did not affect the response to bradykinin. Incubation of the cells with the Ca2+ ionophore A23187 (0.1-1 microM) made the cells unresponsive to bradykinin and, somewhat less, to Ins-P3. At these concentrations the Ca2+ ionophore primarily depletes intracellular Ca2+ stores. In summary, bradykinin, via B2-receptors (blocked by [Thi5,8, D-Phe7]-bradykinin) activates a K+ conductance in glioma cells following a rise of cytosolic Ca2+ activity most likely due to Ins-P3-mediated release of Ca2+ from internal stores. Entry of extracellular Ca2+ appears also to be involved in this process.
authors.affiliation: Physiologisch-chemisches Institut der Universität Tübingen, F.R.G.
authors.forename: G
authors.initials: G
authors.lastname: Reiser
authors.forename: F J
authors.initials: FJ
authors.lastname: Binmöller
authors.forename: P N
authors.initials: PN
authors.lastname: Strong
authors.forename: B
authors.initials: B
authors.lastname: Hamprecht
mesh_terms: D000818:Animals; D001920:Bradykinin / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005910:Glioma; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000502:physiology*; D051381:Rats; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000502:physiology*
chemical_list: D002121:Calcium Channel Blockers; D015544:Inositol 1,4,5-Trisphosphate; D011188:Potassium; D001920:Bradykinin; D002118:Calcium